For example, a user interface for moving a cursor or pointer on a screen needs an operation means. As a method of detecting a user's operation for moving the cursor or the like, there are a method of detecting a movement of an operation site of a user's arm, leg, or finger that is captured by a camera based on a position of the operation site in the image and a method of detecting the movement based on a signal of a gyro sensor attached to the user's arm, leg, or finger.
In the case where the user interface operation for the cursor or pointer is performed using the user's limb, finger, or the like as described above, an external detector such as a camera and a gyro sensor is necessary.
Furthermore, in the case where the operation for moving the cursor or the pointer is performed using the line of sight of the user, it is necessary to detect an eyeball movement of the user.
Examples of the method of measuring a position or movement of the eyeball include a search coil method using the fact that a potential is generated in a coil placed in a magnetic field, the potential being proportional to an angle formed by the magnetic field and the coil. In the search coil method, a detection coil is incorporated in a contact lens. It is worn on an eyeball. A magnetic field coil that applies horizontal and vertical magnetic fields is externally placed. Induced electromotive force is generated in the detection coil incorporated in the contact lens due to the fields applied from the outside. The induced electromotive force is detected. In this manner, the eyeball movement is detected.
As another method of measuring the position or movement of the eyeball, an EOG (Electrooculography) method is also known. The EOG method uses the fact that a cornea has a positive potential of from 10 to 30 μV in comparison with a retina. Electrodes are attached around an eye. A potential difference is detected.
As other methods of measuring the position or movement of the eyeball, a limbus tracking method, a corneal reflection method, and a pupil corneal reflection method are known.
The limbus tracking method uses the feet that the reflectance of infrared light emitted to an eye differs between a sclera and iris and pupil. Light reflected by an eyeball is captured by an externally placed camera. An eyeball movement is thus detected.
Furthermore, the corneal reflection method uses the fact that a virtual image on a cornea portion that is formed of infrared LED light emitted to the eye by an infrared light LED (Light Emitting Diode) is moved in parallel along with an eyeball movement due to a rotation center difference between the cornea portion and the eyeball. The virtual image of the infrared LED light reflected by the eyeball is captured by the externally placed camera. The eyeball movement is thus detected.
The pupil corneal reflection method has the same basic principles as the corneal reflection method. However, the pupil corneal reflection method is different from the corneal reflection method in that the center of the pupil is used as a reference. That is, the pupil corneal reflection method is a method in which the center of the pupil is detected by the externally placed camera and the eyeball movement is detected based on a difference from the position of the virtual image of the infrared LED light.
By the way, as a compact image display apparatus, a contact lens type display apparatus has been proposed (e.g., see Patent Document 1). This display apparatus is used by being worn on an eyeball of the user. Therefore, irrespective of where the user is located, images can be presented to the user.
Patent Document 1: Japanese Patent No. 4752309